162 TJXMyS. 



The best results would probably be obtained by extracting 

 directly Avith alcohol, evaporating the tincture in a partial 

 vacuum, treating the residue with water, quickly filtering and 

 estimating at once Avith gelatine or permanganate of potassium. 

 (Cf. §§ 51, 52, VII. and XII.) In standardizing the solutions, 

 it may be useful to remember that, according to Giinther's 

 experiments, quercitannic acid, though differing greatly in other 

 respects from gallotannic acid, possesses the same cpiantitative 

 action on permanganate of potassium. It must be observed 

 that tannic acid is deposited when its solution is completely 

 saturated with chloride of ammonium ; it is adA'isable, therefore, 

 when precipitating with gelatine, to follow the directions given 

 for titrating catechu-tannic acid. Quercitannic acid is sparingly 

 soluble in ether; ferroso-ferric salts produce inky mixtures with 

 its aqueous solution; other of its properties are mentioned in 

 §§ 49, 51. The lead salt obtained by precipitation Avith a 

 slight excess of the acetate contains 56 to 57 per cent, of oxide, 

 the copper salt 29*5 per cent. The oak-red produced artificially 

 from the tannic acid is identical Avith the phlobaphene that occurs 

 naturally in the bark. It is likeAvise coloured black by iron salts, 

 yields protocatechuic acid and phloroglucin Avhen fused Avith 

 potash, and possesses the jiroperties of a phlobaphene as 

 enumerated in §§ 108, 100. 



The tannins of the jiini','^ hirrJi, many species of acadu, etc., 

 Avhich have been but little investigated, may possibly resemble 

 quercitannic acid in many of their essential characters. 



FilixAannic acid- is resolved, on boiling Avith acids, into glucose 

 and red flocks of filix-red ; the latter closely resembles cinchona- 

 red. 



Cinchona-tannic acid ^ undergoes a similar decomposition Avith 

 production of cinchona-red. Its lead salt is someAvhat easily 

 soluble in acetic acid. 



^ Compare Kawalier, Wiener Akad. Ber. xi. 354 ct seq. ; Rochleder und 

 Kawalier, ibid. xxix. 22 at wi[. ; Wittstein Vierteljahresschr. f. pract. Pharm, 

 iii. 14, 18.54. 



- See Malin, Chem. Centralblatt, xii. 4G8, 1867. For tannaspidic acid and 

 pteritannic acid, the former of which Malin believes to be iiuinue filix-red, see 

 Lvick, ibid. C)?, C76, 1851. Compare further Grabowski, Annal. d. Chem. 

 iind Pharm, cxlii. 279, 1807. 



•* Compare liembold, Annal. d. Chem. nnd Pharm, cxliii, 270, 1867, and 

 Schwarz, Chem. Centralblatt, 193, 1852. 



